Sorry, it is not possible to evaluate thumbnails. For such purpose 600 dpi scans in full scale are necessary. So please release (or sent!) one or two full scale 600 dpi scans, as png or jpg (low compression, 95% or better). I know, big files, but it is important to have the full information.
And some hints: disable all automatic correction in the scan process like color correction, sharpness, contrast (and AUTO TONE, of course). Disable automatic removing of scratches and so on. All these things will lower the quality of the scans.
And don't use an all-in-one scanner. Such devices are only junk and not suitable to get good scans. And don't use a LED scanner. Such a device is completely unsuitable for scanning foil cards. And don't use a cheap scanner (<250 Euro). Using such devices is wasted time.
Clean carefully the scanner surface (and the cards, if necessary) before every scan. Otherwise there will be a lot of dust, decreasing the quality of the result.
Good luck.
BTW, here you'll find a test scan. This illustrate the necessary quality. Scanning in lower quality is wasted time, when you will have great high quality scans in the end, believe me.
http://www.mediafire.com/i/?pqqp6yxfgb1ipig